Hitherto, for obtaining only a specific gas component from a multi-component mixed gas, it has been known to use an organic or inorganic gas separation membrane.
As the separation membrane used for membrane separation method, there have been known organic polymer membranes such as of polyimide and polysulfone as hydrogen separation membranes and inorganic compound membranes such as palladium or palladium alloy membranes. Particularly, palladium or palladium alloy membranes have heat resistance and, furthermore, can give hydrogen of very high purity.
Palladium or palladium alloy membranes have property of permeating hydrogen in the form of a solid solution, and utilizing this property, thin membranes of palladium or palladium alloys are widely used as hydrogen separators for separating hydrogen from a mixed gas containing hydrogen.
As to related conventional techniques, JP-A-62-273030 and JP-A-63-171617 disclose a gas separator comprising a porous substrate, one surface of which is covered with a gas separation membrane comprising palladium or a palladium alloy, in which the porous substrate comprises ceramics such as glass and aluminum oxide. Since the gas separation membrane alone is insufficient in mechanical strength, the gas separation membrane is put on a porous substrate.
A gas separating device having the above gas separator incorporated therein has a structure in which a gas to be treated is introduced from one side of the gas separator, and only a specific gas permeates through the gas separator and purified hydrogen gas is obtained from another side of the gas separator. Therefore, it is important that the side of gas to be treated and the side of purified gas should be air-tightly separated to inhibit leakage of the gas to be treated to the purified gas side from the joint part of the gas separator and the support. On the other hand, in order to efficiently separate hydrogen gas using a gas separator, it is advantageous to carry out the separation at high temperatures and under high pressures, namely, at 300° C. or higher, preferably 500° C. or higher under 5-20 atm for increasing the diffusion rate of hydrogen atom or the like through the gas separation membrane.
In order to inhibit leakage of gas under the above conditions, generally the gas separator and the support are bonded with glass or brazing material (glass bonding, brazing). Furthermore, when the gas treating temperature is lower than 250° C., air-tightness between the gas separator and the support is ensured using an O-ring made of resin or rubber.
However, when the gas separator and the support are bonded by the above-mentioned glass bonding or brazing, there may be supposed occurrence of the problem that the porous substrate constituting the gas separator is broken by thermal stress or air-tightness between the gas separator and the support is lowered with loading of heat cycles. Furthermore, not only the gas separator and the support must be bonded with severely controlling the clearance between them, but also there may occur the problem such as distortion caused by thermal stress because of the high bonding temperature.
In the case of securing the air-tightness between the gas separator and the support using an O-ring made of resin or rubber, when the treating temperature of gas is higher than 250° C., it is substantially difficult to secure sufficient air-tightness, and as a result, the range of operation temperature is restricted.
The present invention has been made in view of these problems in conventional techniques, and the object of the present invention is to provide a gas separator fixing structure and a gas separating device using the same in which the base which constitutes the gas separator is hardly broken by thermal stress and the air-tightness between the gas separator and a support supporting the gas separator is hardly lowered, and which are usable under the conditions of high temperatures.